Fine copper wire for electronic instruments and method of manufacturing the same

ABSTRACT

A fine copper wire for electronic instruments is disclosed which comprises 0.05 to 10 ppm in total amount of either one or not less than two kinds of Ti, Zr, V, Hf, Cr, Ca, Mg, Y and rare-earth elements, 1 to 30 ppm of oxygen and the remainder of Cu. A method of manufacturing therefor is described wherein the hot rolling is given to the ingot obtained by melting and casting in a nonoxidative atmosphere or in vacuum, then stretch processing and at least once or more times of intermediate annealing are repeated to finish to a fixed diameter of wire, and thereafter annealing is carried out under nonoxidative or reducible atmosphere to obtain desired mechanical characteristics.

This application is a continuation of application Ser. No. 07/209,212,filed on Jun. 20, 1988, now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a fine copper wire for electronicinstruments and a method of manufacturing the same. The fine wire issuitable, in particular, as a bonding wire used for the manufacture ofsemiconductors.

In the manufacture of semiconductors such as transistor, IC, etc., afine wire of Au, Al or alloy thereof with a wire diameter of 15 to 100μm or thereunder is used between the electrode pad of Al connected tocircuit elements and the lead of semiconductor for the connection ofcircuit elements on Si chip to external power source and for the givingand taking of external informations.

The fine wire of Al or Al alloy has an advantage in that the bonding tothe electrode pad can be made with the same kind of metal, and is low incost. However, since the ball bond is generally difficult from thereasons of being apt to be oxidized etc., the wedge bond usingsupersonic wave, which is poor in the productivity, has been adopted.Further, the fine wire of Al or Al alloy is poor in the corrosionresistance and, in particular, tends to cause the corrosion in the caseof resin sealing type semiconductor due to the permeation of moisture.Therefore, it is used exclusively for the gas-tight sealing typesemiconductor.

On the other hand, the fine wire of Au is not only excellent in thecorrosion resistance, but also good in the bondability to Al. Therefore,it has an advantage to be utilized for the ball bonding, which is highin the productivity, and is used widely with the resin sealing typesemiconductor as a leader.

However, the material Au is not only conspicuously high in cost, butalso liable to produce a fragile layer of intermetallic compounds, whichis called purple plague, with Al or Al alloy of electrode pad under anenvironment of high temperature. As a result, the deterioration ofbonding strength occurs with the lapse of time and the increase in theresistance of bonded area or, in a serious case, the break-down of wirecomes to occur.

Moreover, the fine wire of Au does not adhere to the interface of resinand the gaps inevitably produced become the paths of moisture to allowit to permeate easily to the portion of electrode pad. Consequently, Alis corroded by Galvanic pair formed between Au and Al and the increasein the resistance of connection and the break-down of wire sometimesoccur similarly to said purple plague. In particular, accompanying withthe high integration and getting larger in size of chip and theminiaturization and pin-multiplication of package, a drastic lowering inthe reliability resulting from the high temperature due to an increasein the density of heat generation, the shortening in the path of watervapor permeation and the increase in the probability of water vaporpermeation is feared.

For these reasons, the development of fine wire which can be substitutedfor the fine wire of Au and the characteristics of which are also equalto or higher than those of fine wire of Au is desired. Although a finewire of Cu is proposed for this purpose, the deformability thereof isinferior to that of Au and such problems that the cracks are generatedunder the electrode pad and the bonding between electrode pad and Al isinsufficient are caused. In particular, with high-integration IC,fragile insulation layers of SiO₂ etc. exist most frequently under theelectrode pad and the development of fine wire of Cu, which has thedeformability of equal to or higher than that of Au, is desired.

With regard to the fine wire of Cu, a fine wire of Cu containing 0.1 to2% (1000 to 20000 ppm) of Be, Sn, Zn, Zr, Cr or Fe in Cu is proposed inJapanese Unexamined Patent Publication No. Sho 57-149744. This isexcellent in the mechanical strength at high temperature, but it is farhard compared with the fine wire of Au. For this reason, excessivemechanical stress is applied to the semiconductor chip or the circuitsubstrate upon bonding resulting in the occurrence of damages of chipsuch as the cracking, cratering, etc.

This fact is particularly remarkable in the ball bonding and the ballformed is joined to the electrode pad on the semiconductor chip by meansof the thermo-sonic method combined with thermal pressing and ultrasonicwave energy. The conditions at this time are temperature of 150° to 350°C., load of 10 to 200 g, output of ultrasonic wave of 10 to 200 mW andtime of 10 to 100 msec. And, the hard ball requires always high bondingconditions, which bring about not only the lowering in the reliabilityand the lowering in the productivity, but also the fatal defect causingsaid cracking.

Furthermore, with regard to the fine wire of Cu, a fine wire of Cucontaining 5 to 20000 ppm of rare-earth elements is proposed in JapaneseUnexamined Patent Publication No. Sho 59-139662, a fine wire of Cucontaining 10 to 20000 ppm of rare-earth elements, alkaline earthelements, Pd, Pt, Au, Bi, Te, Ge, Si, In, Al, B, Cd, Ti, Hf, V, Nb, Tlor Y, in particular, 100 to 10000 ppm of Y, rare-earth elements or Hf isproposed in Japanese Unexamined Patent Publication No. 61-20693, a finewire of Cu containing 5 to 50 ppm of Ti, Cr or Fe or 10 to 100 ppm of Nior Co is proposed in Japanese Unexamined Patent Publication No. Sho61-99645, and a fine wire of Cu containing 5 to 50 ppm of Zr or Nb or 10to 100 ppm of Pd, Ag, In or Sn is proposed in Japanese Unexamined PatentPublication No. Sho 61-99646. All of these are Cu alloys havingrelatively high concentration, though not so much as the fine wire of Cuproposed in Japanese Unexamined Patent Publication No. Sho 57-149744aforementioned, and thus there is a problem in the hardness of ball.According to the experimental experiences by the inventors, the hardnessof the ball of Cu is influenced significantly by the purity, inparticular, the elements that form the solid solution and the purer thesofter. In this respect, RRR (Residual Resistivity Ratio) having spreadas a practical index of the purity of Cu is reasonable as a measure ofbondability. The fine wires of Cu proposed in said Patent Publicationshave RRR of 200 to 500, which is larger than 100 to 300 of tough pitchcopper or oxygen-free copper used ordinarily for the electrical use,nevertheless is an extent being much the same. This fact is insufficientin the industrial use, for which the bonding of LSI or VLSI withparticularly high integration is made at high speed.

As a result of diligent investigations in view of this situation, a finecopper wire for electronic instruments suitable for the bonding wire anda method of manufacturing therefor have been developed by the invention.

SUMMARY OF THE INVENTION

The thin copper wire of the invention is characterized by comprising0.05 to 10 ppm in total amount of either one or not less than two kindsof Ti, Zr, V, Hf, Cr, Ca, Mg, Y and rare-earth elements, 1 to 30 ppm ofoxygen and the remainder of Cu.

Moreover, the manufacturing method of the invention is characterized inthat the alloy comprising 0.05 to 10 ppm in total amount of either oneor not less than two kinds of Ti, Zr, V, Hf, Cr, Ca, Mg, Y andrare-earth elements (RE), 1 to 30 ppm of oxygen and the remainder of Cuis molten and casted in a nonoxidative atmosphere or in vacuum toconvert to the ingot, the hot rolling is given to this, then drawing andat least once or more times of intermediate annealing are repeated tofinish to a fixed diameter of wire, and thereafter annealing is carriedout under a nonoxidative or reducible atmosphere to obtain desiredmechanical characteristics.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the results that, among the breaking modes of fine wireball-bonded to an alloy strip comprising Cu-0.15% Cr-0.1% Sn, the ratesof normal break of wire were compared in terms of the rate of finaldrawing and the elongation of wire.

DETAILED DESCRIPTION OF THE INVENTION

For the wire bonding between semiconductor elements and inner lead, thewedge bond by ultrasonic wave is sometimes used, but there are manyexamples to be ball-bonded. In the ball bonding, the tip of fine wire ismolten by H₂ flame or electric discharge and formed into a ball due tothe surface tension. At this time, the facts that the ball is close tothe real sphere and not eccentric, that the ball is joined easily to thepad of Al which forms the electrode of chip, that the loop of fine wireretains a suitable height and the bonding strength to inner lead issufficient, and the like are necessitated. Particularly, in bonding ofhigh-integration IC where soft bonding conditions such as lower loadingand lower output of ultrasonic wave are requested for the preventionfrom the mechanical damage, so-called cratering, of the chip, thebonding characteristics comparable with those of Au is required.

According to the invention, the requirements as above can be satisfiedby using pure Cu containing 0.05 to 10 ppm in total amount of either oneor not less than two kinds of Ti, Zr, V, Hf, Cr, Ca, Mg, Y andrare-earth elements (RE) and 1 to 30 ppm of coexistent oxygen, inparticular, pure Cu with a purity of not less than 99.999%. In theinvention, the addition of said elements under 0.05 ppm exhibits noeffect and that over 10 ppm is harmful inversely because the ballbecomes hard. Moreover, the existence of oxygen under 1 ppm exhibits noeffect and that over 30 ppm is harmful because it reacts with hydrogenin the atmosphere at the time of ball formation and void is produced inthe ball to lower the reliability of ball bonding. The addition level ofthese varys depending on the purity of matrix Cu and can be made smallerwith an enhancement in the purity.

Moreover, in the manufacture of said fine copper wire of the invention,the hot rolling is given to the ingot obtained by melting and casting ina nonoxidative atmosphere or in vacuum, then drawing and once or moretimes of intermediate annealing are repeated to finish to a fixeddiameter of wire and thereafter annealing is carried out undernonoxidative or reducible atmosphere to obtain desired mechanicalcharacteristics. By doing so, the bonding characteristics comparablewith those of Au can be obtained. In such manufacturing process, if atleast once of intermediate annealing is kept for not shorter than 30minutes at not lower than 500° C., in particular, and thereafter coolingis made to not higher than 300° C. at a speed of not faster than 100° C.per minute, the ball bonding property can be made better further.Moreover, in said process, by making at least the reduction of finaldrawing 70 to 99.99%, preferable 90 to 99.9% and yet by making theelongation 5 to 25%, preferably 8 to 20% through final annealing, thefine copper wire better in the stitch bonding property can be obtained.

The reason why said actions are achieved in the invention is not clear,but, from the facts that the ball becomes harder as the elements thatform the solid solution increase and that the ball bonding propertybecomes better by restricting the addition elements and oxygen to theranges of the invention, it appears that the impurities in matrix Cu arefixed by the addition elements and oxygen. This is backed up also fromthe fact that the ball bonding property is improved by keeping at hightemperature in the intermediate annealing at the time of manufacture.

With regard to the fine copper wire, the shape of loop and the strengthof fine wire are practically important together with the ball and stitchbonding property as described. Although the mechanical characteristicsof fine wire take part in these characteristics, the characteristicsrequired vary depending on the kind of semiconductor device, bondingsystem and conditions. However, if the elongation is conspicuously low,the height of loop becomes high resulting in a cause to give rise to theshort circuit between fine wires. In addition, the deformability of finewire is small and, at the time of making stitch bond or wedge bond, highloading and high output of ultrasonic wave are needed to lower thebonding property. Whereas, if the elongation is conspicuously high, theheight of loop becomes low resulting in a danger to bring about thecontact with chip. Additionally, the collapse of wire at stitch bondbecomes large and the neck portions tend to become fragile. Furthermore,the tail length of wire after bonding becomes non-uniform and such astatus that the formation of ball cannot be made comes to occur. Forthis reason, said mechanical characteristics are effective in practice.

In order to develop these characteristics stably and advantageously inpractice, at least the reduction of final drawing before annealing isnecessary to be nade 70 to 99.99%, preferably 90 to 99.95%, and further,if the elongation is adjusted to 5 to 25%, preferably 8 to 20% byannealing for a fixed time at a temperature of 150° to 400° C., moreexcellent characteristics can be derived.

In following, the invention will be illustrated in more detail based onthe examples.

EXAMPLE 1

Employing a vacuum melting furnace, the addition elements were added topure Cu with a purity of 99.9996% and the ingots (billets with adiameter of 25 mm and a length of 140 mm) having alloy compositionsshown by No. 1 thru 23 in Table 1 were casted. After these ingots wereshaven to make the diameter about 20 mm and the length about 100 mm,they were submitted to hot rolling to make the diameter about 10 mm andthen via the scalping, the drawing was carried out.

In this drawing, the reduction of the drawing of 90% and the annealingat 350° C. were repeated to make the fine wires with a diameter of 25μm. Finally, the running annealing was carried out in argon atmospheremaking the temperature 250° to 400° C. to manufacture the fine wireswith an elongation rate of about 15% ot do. Of these wires, themechanical characteristics immediately after the manufacture and afterthe preservation for a month at room temperature subsequently to themanufacture were examined. Moreover, the fine wires were ball-bonded in10% H₂ -N₂ atmosphere with a manual type wire bonder under the bondingconditions set up as the load is 35 g, output of ultrasanic wave is 0.02W, time is 30 msec and stage temperature is 275° C. to testcomparatively about the following items. These results are shown inTable 2 in comparison with conventional Au wire (FA-25, made by TanakaElectronics). Besides, in Table 2, B1 and E1 indicate the breakingstrength and the elongation, respectively.

(1) Shape of the ball (Degree of real sphere, eccentricity).

(2) Distortion of the ball (Comparison of the ball diameter immediatelyafter the balling-up with that after collapsed).

(3) Unbonded ball (Unsuccess rate of bonding when ball-bonded to Al witha thickness of 1 μm, which was metallized onto Si wafer).

(4) Chip cratering (This was shown by the number of electrode padscaused the crater when ball-bonded using ten 16-pin TTLICs).

(5) Breaking mode of the bonded wire (The position of break-down whenthe wire pull test was conducted after bonding was observed judgingwhether it is at the bonded portion or at the wire cut. Result is shownby the rate (%) of wire breaking).

(6) Shape of the loop (With regard to the height and the lateraldirection of loop after bonding, whether or not the average volue ofslipping-off lies within 1.5 times of the diameter).

Besides, in the cases of items (5) and (6), a plating-free alloy strip(thickness: 0.25 mm) comprising Cu-0.15% Cr-0.1% Sn was used as asubstrate.

                                      TABLE 1                                     __________________________________________________________________________              Composition (ppm)                                                   Fine wire                                                                            No.                                                                              Cu   Ti Zr V  Hf Cr Ca Mg Y  La Ce                                                                              O.sub.2                           __________________________________________________________________________    Fine wire of                                                                          1 Balance                                                                            0.55                                                                             -- -- -- -- -- -- -- -- --                                                                               8                                the invention                                                                 Fine wire of                                                                          2 "    0.82                                                                             -- -- -- -- -- -- -- -- --                                                                              14                                the invention                                                                 Fine wire of                                                                          3 "    0.63                                                                             -- -- -- -- -- -- 1.1                                                                              -- --                                                                              20                                the invention                                                                 Fine wire of                                                                          4 "    1.4                                                                              -- -- -- -- -- -- 0.88                                                                             -- --                                                                               7                                the invention                                                                 Fine wire of                                                                          5 "    0.92                                                                             -- 1.1                                                                              -- -- -- -- -- -- --                                                                              10                                the invention                                                                 Fine wire of                                                                          6 "    0.14                                                                             -- -- -- --  0.14                                                                            -- -- -- --                                                                              12                                the invention                                                                 Fine wire of                                                                          7 "    2.3                                                                              -- -- -- -- -- -- -- 0.91                                                                             --                                                                               4                                the invention                                                                 Fine wire of                                                                          8 "    -- -- -- -- -- -- 0.97                                                                             -- -- --                                                                               8                                the invention                                                                 Fine wire of                                                                          9 "    -- -- -- -- -- -- -- -- 2.9                                                                              --                                                                               4                                the invention                                                                 Fine wire of                                                                         10 "    -- --  0.63                                                                            -- 0.16                                                                             -- -- 0.14                                                                             -- --                                                                              12                                the invention                                                                 Fine wire of                                                                         11 "    -- 2.2                                                                              -- -- -- 1.8                                                                              -- -- -- --                                                                               6                                the invention                                                                 Fine wire of                                                                         12 "    -- -- --  2.2                                                                             -- -- -- -- -- 2.4                                                                             24                                the invention                                                                 Fine wire of                                                                         13 "    -- -- -- -- -- 4.3                                                                              -- -- -- --                                                                              12                                the invention                                                                 Fine wire of                                                                         14 "    --  0.41                                                                            3.9                                                                              -- -- -- -- 3.2                                                                              -- --                                                                               7                                the invention                                                                 Comparative                                                                          15 "    -- -- -- -- -- -- -- -- -- --                                                                               5                                fine wire                                                                     Comparative                                                                          16 "    2.3                                                                              -- -- -- -- -- -- -- -- --                                                                              53                                fine wire                                                                     Comparative                                                                          17 "    -- 1.4                                                                              -- -- -- -- -- 2.2                                                                              -- --                                                                              44                                fine wire                                                                     Comparative                                                                          18 "    -- -- 4.2                                                                              -- -- -- 13.8                                                                             -- -- --                                                                               8                                fine wire                                                                     Comparative                                                                          19 "    -- -- -- 12.4                                                                             -- -- -- 6.3                                                                              -- --                                                                              12                                fine wire                                                                     Comparative                                                                          20 "    -- 40 -- -- 212                                                                              -- -- -- -- --                                                                              23                                fine wire                                                                     Comparative                                                                          21 "    -- -- -- -- -- -- 1640                                                                             -- -- --                                                                              51                                fine wire                                                                     Comparative                                                                          22 "    -- -- 4318                                                                             744                                                                              -- -- -- -- -- --                                                                              18                                fine wire                                                                     Comparative                                                                          23 "    19 27 -- -- 36 -- -- -- -- --                                                                              29                                fine wire                                                                     __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________              Immediately                                                                           After pres-                                                           after   ervation                                                                              Shape  Distortion                                                                          Unbonded                                                                            Shape  Breaking                                                                            Cratering                     manufacture                                                                           for a month                                                                           of     of    rate of                                                                             of     rate                                                                                rate of             Fine wire                                                                            No.                                                                              Bl (g)                                                                            El (%)                                                                            Bl (g)                                                                            El (%)                                                                            ball   ball  ball (%)                                                                            loop   wire                                                                                chip                __________________________________________________________________________                                                              (%)                 Fine wire of                                                                          1 12.4                                                                              14.2                                                                              12.5                                                                              14.1                                                                              Good   0.6   5     Good   100   0                   the invention                                                                 Fine wire of                                                                          2 12.6                                                                              14.7                                                                              12.6                                                                              14.6                                                                              "      0.7   4     "      "     "                   the invention                                                                 Fine wire of                                                                          3 12.4                                                                              15.1                                                                              12.3                                                                              15.2                                                                              "      0.7   5     "      "     "                   the invention                                                                 Fine wire of                                                                          4 12.4                                                                              14.8                                                                              12.4                                                                              14.9                                                                              "      0.6   5     "      "     "                   the invention                                                                 Fine wire of                                                                          5 12.5                                                                              14.7                                                                              12.4                                                                              14.7                                                                              "      0.7   4     "      "     "                   the invention                                                                 Fine wire of                                                                          6 12.7                                                                              13.9                                                                              12.6                                                                              14.1                                                                              "      0.7   6     "      "     "                   the invention                                                                 Fine wire of                                                                          7 12.4                                                                              14.8                                                                              12.6                                                                              14.7                                                                              "      0.7   5     "      "     "                   the invention                                                                 Fine wire of                                                                          8 12.2                                                                              14.5                                                                              12.3                                                                              14.7                                                                              "      0.6   4     "      "     "                   the invention                                                                 Fine wire of                                                                          9 12.6                                                                              15.8                                                                              12.6                                                                              14.7                                                                              "      0.7   6     "      "     "                   the invention                                                                 Fine wire of                                                                         10 12.6                                                                              14.1                                                                              12.5                                                                              14.3                                                                              "      0.8   6     "      "     "                   the invention                                                                 Fine wire of                                                                         11 12.8                                                                              13.8                                                                              12.7                                                                              13.8                                                                              "      0.7   4     "      "     "                   the invention                                                                 Fine wire of                                                                         12 12.6                                                                              14.2                                                                              12.5                                                                              14.2                                                                              "      0.7   5     "      "     "                   the invention                                                                 Fine wire of                                                                         13 12.7                                                                              13.7                                                                              12.6                                                                              12.6                                                                              "      0.6   6     "      "     "                   the invention                                                                 Fine wire of                                                                         14 12.5                                                                              14.5                                                                              12.5                                                                              12.6                                                                              "      0.7   6     "      "     "                   the invention                                                                 Comparative                                                                          15 12.4                                                                              14.7                                                                              11.9                                                                              16.4                                                                              Slightly poor                                                                        0.4   18    Slightly poor                                                                         98   6                   fine wire                                                                     Comparative                                                                          16 12.5                                                                              14.4                                                                              12.4                                                                              14.5                                                                              Poor (void)                                                                          --    --    --     --    --                  fine wire                                                                     Comparative                                                                          17 12.2                                                                              13.6                                                                              12.3                                                                              13.7                                                                              Poor (void)                                                                          --    --    --     --    --                  fine wire                                                                     Comparative                                                                          18 12.6                                                                              14.3                                                                              12.5                                                                              14.2                                                                              Slightly poor                                                                        0.6   9     Slightly poor                                                                        100   4                   fine wire                                                                     Comparative                                                                          19 12.3                                                                              14.1                                                                              12.3                                                                              14.2                                                                              "      0.6   8     "      "     6                   fine wire                                                                     Comparative                                                                          20 12.4                                                                              14.8                                                                              12.4                                                                              14.9                                                                              "      0.4   27    "       71   13                  fine wire                                                                     Comparative                                                                          21 12.4                                                                              14.1                                                                              12.3                                                                              14.5                                                                              Poor (void)                                                                          --    --    --     --    --                  fine wire                                                                     Comparative                                                                          22 12.7                                                                              14.0                                                                              12.6                                                                              14.2                                                                              Poor   --    --    --     --    --                  fine wire                                                                     Comparative                                                                          23 12.3                                                                              15.2                                                                              12.3                                                                              15.3                                                                              Slightly poor                                                                        0.4   36    Slightly poor                                                                         83   18                  fine wire                                                                     Au wire                                                                              24 12.1                                                                               4.1                                                                              12.2                                                                               4.3                                                                              Good   0.6   5     Good   100   0                   __________________________________________________________________________

As evident from Table 1 and Table 2, it can be seen that, with all ofthe fine wires of the invention No. 1 thru No. 14, results equal toconventional Au wire can be obtained. On the contrary, with comparativefine wire No. 15 without the addition ingredients, not only the bondingproperty is poor, but also the change of characteristics is caused uponthe preservation at normal temperature, which results a significantinsecure factor in the industrial utilization. Moreover, in the cases ofcomparative fine wires No. 16, No. 17 and No. 21 in which the contentsof sxygen are excess, void is produced in the ball, and in the cases ofcomparative fine wires No. 18, No. 19, No. 20, No. 22 and No. 23 inwhich the addition elements are excess, unbonded ball and cratering arecaused resulting in the poor bonding property.

EXAMPLE 2

Using pure Cu with a purity of 99.99998%, the fine copper wires with adiameter of 25 μm, which had the compositions shown in Table 3, weremanufactured similarly to Example 1. These were ball-bonded to the leadframe (thickness: 0.2 mm, width: 33.02 mm) comprising Cu-0.15% Cr-0.1%Sn alloy, which carried 42-pin LOGIC IC, with an auto-bonder(SWB-FA-CUB-10, made by Shinkawa) to evaluate the fine copper wires. Theresults are shown in Table 4 in comparison with conventional Au wire(FA-25, made by Tanaka Electronics).

                                      TABLE 3                                     __________________________________________________________________________              Composition (ppm)                                                   Thin Wire                                                                            No.                                                                              Cu   Ti Zr V  Hf Cr Ca Mg Y  La Ce O.sub.2                          __________________________________________________________________________    Thin wire of                                                                         25 Balance                                                                            0.06                                                                             -- -- -- -- -- -- -- -- --  3                               the invention                                                                 Thin wire of                                                                         26 "    0.74                                                                             -- -- -- -- -- -- -- -- -- 18                               the invention                                                                 Thin wire of                                                                         27 "    1.2                                                                              -- -- -- -- -- -- 0.95                                                                             -- --  9                               the invention                                                                 Thin wire of                                                                         28 "    0.98                                                                             -- -- -- -- -- -- 1.7                                                                              -- -- 12                               the invention                                                                 Thin wire of                                                                         29 "    0.63                                                                             -- 0.86                                                                             -- -- -- -- -- -- -- 15                               the invention                                                                 Thin wire of                                                                         30 "    0.04                                                                             -- -- -- -- 0.12                                                                             -- -- -- -- 12                               the invention                                                                 Thin wire of                                                                         31 "    -- -- 0.04                                                                             -- -- -- -- 0.06                                                                             -- -- 14                               the invention                                                                 Thin wire of                                                                         32 "    -- 1.2                                                                              -- -- -- -- 0.13                                                                             -- -- --  5                               the invention                                                                 Thin wire of                                                                         33 "    -- -- -- 0.42                                                                             -- 0.13                                                                             -- -- -- --  4                               the invention                                                                 Thin wire of                                                                         34 "    2.1                                                                              -- -- -- -- -- -- -- 0.42                                                                             -- 23                               the invention                                                                 Thin wire of                                                                         35 "    -- -- 0.96                                                                             -- -- -- -- -- -- 0.27                                                                              8                               the invention                                                                 Thin wire of                                                                         36 "    -- -- -- -- 5.2                                                                              -- -- -- -- -- 14                               the invention                                                                 Thin wire of                                                                         37 "    --  0.03                                                                            -- -- -- -- -- -- 0.04                                                                             -- 26                               the invention                                                                 Thin wire of                                                                         38 "    -- -- -- 6.2                                                                              -- -- -- 2.4                                                                              -- -- 13                               the invention                                                                 Comparative                                                                          39 "    -- -- -- -- -- -- -- -- -- -- 13                               fine wire                                                                     Comparative                                                                          40 "    0.13                                                                             -- -- -- -- -- -- 0.24                                                                             -- -- 44                               fine wire                                                                     Comparative                                                                          41 "    -- -- 1.3                                                                              -- -- -- -- -- 0.64                                                                             -- 53                               fine wire                                                                     Comparative                                                                          42 "    -- 4.6                                                                              -- -- -- -- -- 13.8                                                                             -- -- 23                               fine wire                                                                     Comparative                                                                          43 "    -- -- -- -- 5.7                                                                              -- -- -- -- 14.1                                                                             12                               fine wire                                                                     Comparative                                                                          44 "    -- -- -- -- -- -- 2617                                                                             -- -- -- 18                               fine wire                                                                     Comparative                                                                          45 "    -- 76 -- -- -- 664                                                                              -- -- 379                                                                              -- 24                               fine wire                                                                     Comparative                                                                          46 "    -- -- 120                                                                              -- 477                                                                              -- -- -- -- -- 15                               fine wire                                                                     __________________________________________________________________________

                                      TABLE 4                                     __________________________________________________________________________              Bl El                Cratering rate                                                                        Breaking rate                          Fine wire                                                                            No.                                                                              (g)                                                                              (%)                                                                              Shape of ball                                                                         Shape of loop                                                                        of chip (%)                                                                           of wire (%)                            __________________________________________________________________________    Fine wire of                                                                         25 12.4                                                                             14.3                                                                             Good    Good   1       98                                     the invention                                                                 Fine wire of                                                                         26 12.4                                                                             14.3                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         27 12.4                                                                             14.4                                                                             "       "      0       "                                      the invention                                                                 Fine wire of                                                                         28 12.5                                                                             14.4                                                                             "       "      1       "                                      the invention                                                                 Fine wire of                                                                         29 12.6                                                                             14.8                                                                             "       "      1       99                                     the invention                                                                 Fine wire of                                                                         30 12.6                                                                             14.4                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         31 12.4                                                                             14.3                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         32 12.3                                                                             14.4                                                                             "       "      1       99                                     the invention                                                                 Fine wire of                                                                         33 12.3                                                                             14.2                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         34 12.3                                                                             14.1                                                                             "       "      1       97                                     the invention                                                                 Fine wire of                                                                         35 12.5                                                                             14.6                                                                             "       "      1       99                                     the invention                                                                 Fine wire of                                                                         36 12.6                                                                             14.5                                                                             "       "      2       98                                     the invention                                                                 Fine wire of                                                                         37 12.6                                                                             14.7                                                                             "       "      1       98                                     the invention                                                                 Fine wire of                                                                         38 12.4                                                                             14.6                                                                             "       "      2       98                                     the invention                                                                 Comparative                                                                          39 12.6                                                                             14.3                                                                             Slightly poor                                                                         Slightly poor                                                                        16      77                                     fine wire                                                                     Comparative                                                                          40 12.5                                                                             14.7                                                                             Slightly poor                                                                         "      18      91                                     fine wire       (void appeared)                                               Comparative                                                                          41 12.6                                                                             14.5                                                                             Slightly poor                                                                         "      12      92                                     fine wire       (void appeared)                                               Comparative                                                                          42 12.4                                                                             14.3                                                                             Slightly poor                                                                         "      14      95                                     fine wire                                                                     Comparative                                                                          43 12.4                                                                             14.3                                                                             "       "      6       94                                     fine wire                                                                     Comparative                                                                          44 12.5                                                                             14.4                                                                             "       "      34      68                                     fine wire                                                                     Comparative                                                                          45 12.7                                                                             14.8                                                                             "       "      28      78                                     fine wire                                                                     Comparative                                                                          46 12.4                                                                             14.6                                                                             "       "      27      72                                     fine wire                                                                     Au wire                                                                              24 12.1                                                                              4.1                                                                             Good    Good   0       100                                    __________________________________________________________________________

As evident from Table 3 and Table 4, with all of the fine wires of theinvention No. 25 thru No. 38, good shape of the ball was obtained andthe cratering rate of chip was also low. Whereas, in the cases ofcomparative fine wire No. 39 without the addition ingredients,comparative fine wires No. 40 and No. 41 with higher content of oxygenand comparative fine wires No. 42-No. 46 with excess additioningredients it can be seen that the cratering of chip and the breakingof wire occur more frequently.

EXAMPLE 3

In Example 2, during the drawing, the wires with a diameter of 0.8 mmwere annealed for 1 hour at 550° C. in Ar gas, cooled to 300° C. at aspeed of 45° C./min, and then finished to the fine wires with a diameterof 25 μm similarly to Example 2 to make wire bonding.

The results are shown in Table 5 comparing with conventional Au wire(FA-25, made by Tanaka Electronics).

                                      TABLE 5                                     __________________________________________________________________________              Bl El                Cratering rate                                                                        Breaking rate                          Fine wire                                                                            No.                                                                              (g)                                                                              (%)                                                                              Shape of ball                                                                         Shape of loop                                                                        of chip (%)                                                                           of wire (%)                            __________________________________________________________________________    Fine wire of                                                                         25 12.6                                                                             14.6                                                                             Good    Good   0       100                                    the invention                                                                 Fine wire of                                                                         30 12.7                                                                             14.7                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         31 12.5                                                                             14.7                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         32 12.4                                                                             14.3                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         33 12.6                                                                             14.4                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         34 13.1                                                                             14.2                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         35 12.8                                                                             14.6                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         36 12.7                                                                             14.5                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         37 12.8                                                                             14.6                                                                             "       "      0       100                                    the invention                                                                 Fine wire of                                                                         38 12.7                                                                             14.7                                                                             "       "      0       100                                    the invention                                                                 Comparative                                                                          39 12.6                                                                             14.4                                                                             Slightly poor                                                                         Low    8        86                                    fine wire                                                                     Comparative                                                                          40 12.7                                                                             14.6                                                                             "       Good   12       93                                    fine wire                                                                     Comparative                                                                          41 12.8                                                                             14.8                                                                             "       "      14       95                                    fine wire                                                                     Comparative                                                                          42 12.5                                                                             14.6                                                                             "       "      7        94                                    fine wire                                                                     Comparative                                                                          43 12.5                                                                             14.5                                                                             "       "      4        97                                    fine wire                                                                     Au wire                                                                              24 12.1                                                                              4.1                                                                             Good    "      0       100                                    __________________________________________________________________________

As evident from the comparison of Table 4 with Table 5, it can be seenthat, with the fine wires of the invention No. 25 thru No. 38 withoutNo. 26 thru No. 29 wherein at least onece of intermediate annealingduring the stretch processing was conducted by heating for hot shorterthan 30 minutes at not lower than 500° C. and then cooling was made tonot higher than 300° C. at a speed of not faster than 100° C./min, thecratering rate of chip and the breaking rate of wire are furtherimproved.

EXAMPLE 4

In Example 1, the fine wire of the invention No. 8 was annealed duringthe stretch processing at a wire diameter of 0.8 mm in Ar gas under theconditions shown in Table 6 and other processings were kept similarly toExample 1 to convert to the fine wires with a diameter of 25 μm. Thesewere evaluated similarly to Example 2. The results are listed togetherin Table 6.

Besides, the cooling velocity in the table indicates an average coolingvelocity to 300° C.

                                      TABLE 6                                     __________________________________________________________________________              Annealing conditions                                                          Tempera-                                                                              Cooling                                                                            Shape                                                                             Distortion                                                                          Shape                                                                             Unbonded                                                                            Breaking                                                                           Cratering                               ture Time                                                                             velocity                                                                           of  of    of  rate of                                                                             rate of                                                                            rate of                       Fine wire                                                                            No.                                                                              (°C.)                                                                       (hr)                                                                             (°C./min)                                                                   ball                                                                              ball  loop                                                                              ball (%)                                                                            wire (%)                                                                           chip (%)                      __________________________________________________________________________    Fine wire of                                                                         8-1                                                                              550  4   82  Good                                                                              0.7   Good                                                                              0     100  0                             the invention                                                                 Fine wire of                                                                         8-2                                                                              625  0.7                                                                               54  "   0.7   "   0     "    0                             the invention                                                                 Fine wire of                                                                         8-3                                                                              625  1.5                                                                               63  "   0.8   "   0     "    0                             the invention                                                                 Fine wire of                                                                         8-4                                                                              850  1   48  "   0.7   "   0     "    0                             the invention                                                                 Comparative                                                                          8-5                                                                              450  1  120  "   0.7   "   6     "    1                             fine wire                                                                     Comparative                                                                          8-6                                                                              625  1  153  "   0.6   "   5     "    2                             fine wire                                                                     Comparative                                                                          8-7                                                                              625  0.3                                                                              147  "   0.7   "   7     "    1                             fine wire                                                                     Comparative                                                                          8-8                                                                              850  1  169  "   0.6   "   6     "    2                             fine wire                                                                     __________________________________________________________________________

As evident from Table 6, it can be seen that, when at least once ofannealing was conducted during the drawing by heating for not shorterthan 30 minutes at a temperature of not lower than 550° C. and coolingwas made to not higher than 300° C. at a speed of not faster than 100°C./min, the unbonded rate of ball is decreased and the bonding propertyis improved.

EXAMPLE 5

In the manufacture of the fine wire of the invention No. 30 in Example2, the fine wires having various elongations were produced by varyingthe final annealing temperature as well as making the reduction of finaldrawing 60, 80, 90, 95 and 99.99%. These were ball-bonded to a unplatedalloy strip (thickness: 0.25 mm) comprising Cu-0.15% Cr-0.1% Snsimilarly to Example 1 and the pull test thereof was conducted todetermined the rate of breaking mode of fine wire. Results are shown inFIG. 1.

As evident from the figure, it can be seen that good bondingcharacteristics can be obtained at high reduction and within a range ofthe elongation of 5 to 25%.

EXAMPLE 6

In Example 3, using the fine wires of the invention No. 30 and No. 35,comparative fine wires No. 39 and No. 41 and conventional Au wire No.24, the resin sealing according to the transfer mold method was carriedout after the wire bonding. Thereafter, the high-temperature heatingtest for 1000 hours at 180° C. and the PC test under the conditions of121° C. and 85% RH were performed. The number of tests was made about50. The results of high-temperature heating test (number of failures),the results of PC test (number of failures) and the classification offailure modes are shown in Table 7, Table 8 and Table 9, respectively.

                  TABLE 7                                                         ______________________________________                                                   Time (hr)                                                          Fine wire                                                                              No.     0       100   300   600   1000                               ______________________________________                                        Fine wire of                                                                           30      0/50    0/50  0/50  0/50  0/50                               the invention                                                                 Fine wire of                                                                           35      0/50    0/50  0/50  0/50  0/50                               the invention                                                                 Comparative                                                                            39      3/50    3/50  3/50  4/50  4/50                               fine wire                                                                     Comparative                                                                            41      5/50    5/50  5/50  5/50  7/50                               fine wire                                                                     Au wire  24      0/50    0/50  1/50  3/50  8/50                               ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                                   Time (hr)                                                          Fine wire                                                                              No.     0       100   300   600   1000                               ______________________________________                                        Fine wire of                                                                           30      0/50    0/50  0/50  0/50  0/50                               the invention                                                                 Fine wire of                                                                           35      0/50    0/50  0/50  0/50  0/50                               the invention                                                                 Comparative                                                                            39      2/50    2/50  2/50  2/50  2/50                               fine wire                                                                     Comparative                                                                            41      5/50    5/50  5/50  5/50  6/50                               fine wire                                                                     Au wire  24      0/50    1/50  1/50  3/50  8/50                               ______________________________________                                    

                                      TABLE 9                                     __________________________________________________________________________              High-temperature heating                                                                    PCT                                                             Short                                                                             Increase in                                                                         Wire                                                                              Short                                                                             Increase in                                                                         Wire                                        Fine wire                                                                            No.                                                                              circuit                                                                           resistance*                                                                         break                                                                             circuit                                                                           resistance*                                                                         break                                       __________________________________________________________________________    Fine wire of                                                                         30 0   0     0   0   0     0                                           the invention                                                                 Fine wire of                                                                         35 0   0     0   0   0     0                                           the invention                                                                 Comparative                                                                          39 3   1     0   2   0     0                                           fine wire                                                                     Comparative                                                                          41 0   1     3   0   1     5                                           fine wire                                                                     Au wire                                                                              24 0   6     2   0   7     1                                           __________________________________________________________________________     *Fine increased by 50% more than rated value.                            

As evident from Table 7, Table 8 and Table 9, the fine wires of thisinvention No. 30 and No. 35 show good results in respective tests, butthe comparative fine wires No. 39 and No. 41 are seen the failures beingmore frequent. Namely, with comparative fine wire No. 39, the failurewas the short circuit due to the deformation of wire at the time ofmolding and, with comparative fine wire No. 41, it was mainly thebreak-down of wire due to the cracking of chip. On the other hand, withconventional Au wire No. 24, it was the purple plague accompanying withthe diffusion of Au and Al through high-temperature heating and, in PCT,it was the damage of Al of electrode pad by corrosion due to thepermeation of moisture, though there occurred also the diffusion.

In this way, the fine wire of the invention is not only excellent in thedeformability, but also high in the wire strength, and it does notsoften at normal temperature and does not cause the droop of loop.Moreover, it exerts excellent effects that the bondability to Al ofelectrode pad is good in the ball bonding and the unbonded rate of ballis low. Furthermore, in accordance with the fine wire of the invention,the bonding characteristics more than equal to those of gold can beobtained also in the ball bond of high-integrated IC for which lowloading and low output of ultrasonic wave are requested, because themechanical damages of chip can be prevented.

As described, the fine wire of the invention is a fruit obtained bypursuing the characteristics of high-purity Cu. With regard to thelong-term reliability besides said effects, it is known, as describedabove, that Al/Au forms a fragile interfacial layer through thediffusion in solid phase and tends to occur the purple plaguephenomenon, but, in the case of Al/Cu, the occurrence is below oneseveralth compared with this. In this sense, too, the effect isextremely significant. For said reasons and others, the invention exertsremarkable effects industrially.

What is claimed is:
 1. A method of manufacturing fine copper wire forelectronic instruments, said wire comprising an alloy comprising 0.05-10ppm in total amount of one or more of Ti, Zr, V, Hf, Cr, Ca, Mg, Y andrare-earth elements, 1-30 ppm of Oxygen and the remainder of Cu, whichprocess comprises:(a) melting and casting said alloy in a non-oxidativeatmosphere or in a vacuum to form an ingot, (b) hot rolling said ingot,(c) drawing said ingot and subjecting the drawn ingot to at least oneintermediate annealing to form a fixed diameter of wire, and (d)annealing said wire under a non-oxidative or reducible atmosphere. 2.The method of claim 1, wherein said at least one intermediate annealingis conducted by heating said ingot for not shorter than 30 minutes atnot lower than 500° C. and then cooling the ingot at not higher than300° C. at a speed of not faster than 100° C. per minute.
 3. The methodof claim 1, wherein the reduction in final drawing is made 70-99.99%. 4.The method of claim 1, wherein the elongation of fine wire is made 5-25%by means of the annealing after finishing to a fixed diameter of wire.